1. Field of the Invention
The present invention relates to a piezoelectric element having an electromechanical conversion function. In particular, the present invention relates to a piezoelectric element that makes it possible to obtain an excellent piezoelectric characteristic when used in an ink-jet recording head, a method for the manufacture thereof, and an ink-jet recording head and a printer using such piezoelectric elements.
2. Description of the Related Art
Ink-jet recording heads use piezoelectric elements as driving mechanism for ink ejection in printers. The piezoelectric elements usually comprise a piezoelectric thin film and a top electrode and a bottom electrode disposed so as to sandwich the film.
Piezoelectric elements with improved characteristics have been developed by regulating the crystal structure of a thin film composed of lead zirconium titanate (PZT) or forming Ti nuclei on the bottom electrode. For example, Japanese Patent Application Laid-open No. H10-81016 disclosed a PZT thin film provided with a rhombohedral crystal structure and the prescribed orientation degree. Furthermore, Japanese Patent Application Laid-open No. H8-335676 disclosed a piezoelectric element in which a titanium nucleus was formed on an Ir bottom electrode.
However, the problem associated with the conventional piezoelectric elements was that piezoelectric films with prescribed orientation degree were difficult to obtain with good stability and reproducibility. Such piezoelectric elements could not provide stable and good piezoelectric characteristics and accounted for insufficient printing performance of ink-jet recording heads or printers.
The prescribed orientation degree of piezoelectric film was especially difficult to obtain with good stability and reproducibility when a bottom electrode formed on a diaphragm was patterned to the prescribed shape and then a piezoelectric film was formed on the bottom electrode. Another problem was that the thickness of the bottom electrode became non-uniform and the crystals of the piezoelectric film became discontinuous in the vicinity of the patterning boundary of bottom electrode.
Accordingly, it is an object of the present invention to provide a piezoelectric element with stable and good piezoelectric characteristic by obtaining the prescribed orientation degree of piezoelectric film with good stability and reproducibility and also a method for the manufacture of such a piezoelectric element. Another object of the present invention is to provide a piezoelectric element demonstrating excellent characteristics by improving the uniformity of the bottom electrode thickness and eliminating the discontinuity of crystals of the piezoelectric film and also a method for the manufacture of such a piezoelectric element.
Still another object is to provide an ink-jet recording head employing the aforesaid piezoelectric elements as ink ejection drive mechanism, a method for the manufacture thereof, and an ink-jet printer.
A method for the manufacture of a piezoelectric element in accordance with the present invention comprises a step of forming a diaphragm on a substrate, a step of forming a bottom electrode on the diaphragm, a step of forming a first piezoelectric layer constituting a part of a piezoelectric film on the bottom electrode, a step of patterning the first piezoelectric layer and the bottom electrode to the prescribed shape, a step of forming a second piezoelectric layer constituting another part of the piezoelectric film on the first piezoelectric layer that was left by the patterning and the diaphragm from which the first piezoelectric layer was removed, and a step of forming a top electrode on the piezoelectric film.
Forming a piezoelectric film in two stages makes it possible to form PZT having stable 100 plane orientation degree which is not affected by humidity or the like. Furthermore, the non-uniformity of the bottom electrode thickness and discontinuity of piezoelectric crystals can be prevented.
Another method for the manufacture of a piezoelectric element in accordance with the present invention comprises a step of forming a diaphragm on a substrate, a step of forming a bottom electrode on the diaphragm, a step of forming a first Ti layer on the bottom electrode, a step of patterning the bottom electrode to the prescribed shape, a step of forming a second Ti layer on the bottom electrode that was left by the patterning and the diaphragm from which the bottom electrode was removed, a step of forming a piezoelectric film on the bottom electrode on which the second Ti layer was formed, and a step of forming a top electrode on the piezoelectric film.
Forming a Ti layer in two stages makes it possible to form a piezoelectric film having a stable 100 plane orientation degree which is not affected by humidity or the like.
A method for the manufacture of an ink-jet recording head in accordance with the present invention comprises a step of etching the substrate of the piezoelectric element obtained by the above-described method and forming pressure chambers and a step of forming a nozzle plate covering the pressure chambers.
In the piezoelectric element in accordance with the present invention, a diaphragm, a bottom electrode, a piezoelectric film, and a top electrode are successively stacked on a substrate. The bottom electrode is patterned to a prescribed shape, and the piezoelectric film is formed on the bottom electrode that was left by the patterning and the diaphragm from which the bottom electrode was removed. The number of layers in the portion of the piezoelectric film, which was formed on the bottom electrode that was left by the patterning, is greater than that in the portion formed on the diaphragm.
Furthermore, in another piezoelectric element in accordance with the present invention, the piezoelectric film is formed on the bottom electrode left by the patterning and on the diaphragm from which the bottom electrode was removed and the thickness of the bottom electrode is uniform.
In still another piezoelectric element in accordance with the present invention, the piezoelectric film is formed on the bottom electrodes left by the patterning and on the diaphragm from which the bottom electrode was removed. The portion of the piezoelectric film that was formed on the diaphragm has a prescribed orientation.
In the above-described piezoelectric element, a portion of the piezoelectric film, which was formed on the bottom electrode that was left by the patterning, preferably has a 100 plane orientation degree of no less than 70%.
The ink-jet recording head in accordance with the present invention comprises the above-described piezoelectric elements, pressure chambers whose internal volume changes under the effect of mechanical displacement of the piezoelectric elements, and ejection openings linked to the pressure chambers and ejecting ink droplets.
The ink-jet printer in accordance with the present invention comprises the above-described ink-jet recording head in a printing mechanism.
The term xe2x80x9c100 plane orientation degreexe2x80x9d used in the present specification means a ratio of I(100) to a sum of I(100), I(110), and I(111), where I(XYZ) stands for a diffraction intensity of a peak (2xcex8) corresponding to a XYZ plane when a CuKxcex1 beam is used in the X ray wide-angle diffraction method.